The present invention relates to compositions of matter for thermoplastic nanocomposites containing nanodiamond particulates known commonly as detonation nanodiamond.
Although detonation nanodiamond (DND) was discovered relatively early (in the 1960's) in USSR as compared to other carbon nanoparticles, viz. fullerenes, single-walled, double-walled, multi-walled carbon nanotubes (SWNT, DWNT and MWNT) and nanofiber (CNF), DND has received little or no attention until 1988 when two landmark papers appeared in open literature. Detonation nanodiamond was so-named because of its production by detonation of 2,4,6-trinitrotoluene (TNT)/1,3,5-trinitro-triazacyclohexane (hexogen) explosives in a closed steel chamber either in gaseous atmosphere, e.g. CO2 (dry method) or in water (wet method). DND is also known by two other common names, viz. ultra-dispersed diamond (UDD) and ultrananocrystalline diamond (UNCD) particulates, because the basic constituents (primary particles) have the characteristic size in the range of 2-10 nm (ave. diameter ˜4-5 nm) and very large specific surface area (>>200 m2/g). With the important advantages such as availability in larger quantities (industrial production capabilities existing in Russia, Ukraine, China and Belarus) and at moderate cost, DND is very attractive as a material platform for nanotechnology. Furthermore, DND has been shown to be non-cytotoxic and biocompatible. These features give DND an additional appeal to bio-related applications in view of its rich surface chemistry that could be modified with relative ease. The surface functional groups identified by various spectroscopic techniques are mostly oxygenated moieties such as —CO2H (carboxylic acid), lactone, C═O (keto carbonyl), —C—O—C (ether) and —OH (hydroxyl). In addition, inter-particle hydrogen-bonding and formation of ester, ether, and anhydride bonds are believed to play important roles in assembling the DND primary particles into much larger aggregates with sizes ranging from a few hundred nanometers (“core agglutinates”) to a few ten microns (“agglomerates”). In fact, under appropriate pH conditions, these inter-particle binding forces are believed to be responsible for the large-scale self-assembly of acid-treated DND into fibers and thin films from drying the suspension. Further, the primary particles in the core agglutinates are so strongly bound together that the total binding force is even greater than that in SWNT ropes, which stems from noncovalent (van deer Waals and π-π) interactions between individual nanotubes. Indeed, it is known that even powerful ultrasonication of crude nanodiamond aggregates could only produce core agglutinates with average size of 120 nm.
Covalent surface modifications of diamond nanoparticles are generally focused on improving the DND processability and introducing suitable functional groups to impart, enhance or tailor certain properties, and eventually, to increase system compatibility and performance. The synthetic tools for such modification have entailed the conversion of the oxygenated groups (i.e. carboxylic acid, hydroxyl etc.) to suitable functionalities for subsequent manipulation. For example, DND was fluorinated using a F2/H2 mixture to afford 8.6 atom % fluorine (replacing OH, CO2H etc.) on the surface, and the fluorinated DND was then used as a precursor for the preparation of alkyl-, amino-, and acid-functionalized DNDs that showed an increased solubility in polar solvents and much smaller size in nanoparticle agglomeration, or coated covalently onto an amine-functionalized glass surface. High temperature (400-850° C.) treatment of DND powders in the presence of H2, Cl2 or NH3 has also led to converting the surface carboxylic acid to alcohol, acid chloride, and nitrile, in that order. More recently, the reduction of the surface —CO2H by BH3.THF complex to the corresponding —CH2OH, followed by O-silylation with (3-aminopropyl)trimethoxysilane and coupling with biotin or a short peptide to generate promising bio-nano hybrid materials has been reported.
Besides the aforementioned reports on the covalent functionalization of DND surfaces that were likely to have occurred at the outermost layer with mixed sp2 and sp3 carbons, Li et al. (Li, L.; Davidson, J. L.; Lukehart, C. M. Carbon 2006, 44, 2308) reported the first example of DND-polymer nanocomposites, in which poly(methyl methacrylate) brushes were grafted from initiators, previously and covalently bonded on the DND surface, by atom transfer radical polymerization (ATRP) process. Most recently, Zhang et al. (Zhang, Q.; Natio, K.; Tanaka, Y.; Kagawa, Y. Macromolecules 2008, 41, 536) reported the grafting of aromatic polyimides from nanodiamonds. In these reports, the DND component in the polymer nanocomposites was actually aggregates (20-50 nm) of primary particles, resulting in polymer-DND particles with sizes 100-200 nm.
Conceptually, there are three general techniques for dispersing chemically unmodified DND in the linear polymer matrices: (1) melt blending (2) solution blending, and (3) reaction blending. For the reaction blending route, there are two scenarios: (a) in-situ polymerization of monomers (AB) or co-monomers (AA+BB) in the presence of dispersed DND that occurs without forming any covalent bonding between the DND and the matrix polymer, or (b) in-situ grafting of AB monomers that occurs with direct covalent bonds formed between the DND and the matrix polymer. Thus, using Friedel-Crafts acylation as a synthetic tool to exemplify reaction blending route to DND-based nanocomposites, it is shown here how to chemically attach meta-poly(ether-ketone) onto the surfaces of DND via in-situ polymerization of an appropriate AB monomer such as m-phenoxybenzoic acid in the presence of DND in poly(phosphoric acid).
Accordingly, it is an object of the present invention to provide a process for attaching a poly(ether-ketone) onto the surfaces of diamond nanoparticles.
It is another object of this invention to provide polymer-grafted nanodiamonds particles and associated nanocomposites.
Other objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.